Blood: Lymphocytes and Monocytes

Blood (Latin: sanguis, Greek: haima) is a suspension of cells in a saline solution containing protein. It makes up 6-8 % of the total body weight and has a pH value of 7.4. The blood carries out many essential functions and is the pivotal point of the whole organism. The following article provides, at a glance, the most important facts about this vital body fluid called blood.

00:00
or that antigen. Let us move on to the
agranulocytes, the lymphocytes.
00:06
I am going to talk about these cells later
on when we talk about the immune system.
00:13
They are very common in blood. They occupy about
28 to 30 percent. So when you look at bloodsmears, you can see a number of this different
sorts of lymphocytes. When they are travelingin blood, they are immunocompetent. But they
are waiting to be attracted and identifyantigens in tissues. So they actually continually
leave the blood through lymph nodes that Iwill talk about in a later lecture. They circulate
through the lymph node, being immunocompetentthat recognized the antigens. They have
been designed to recognize and take care ofan antigen or at least initiate that immune
response against an antigen. If they don'tcome across the antigens, they can leave the
lymph node and then they can get into theblood system and recirculate through the body
again looking for these foreign antigens.
01:14
They are on surveillance duty, but they do
not do their job in blood. They only use bloodto transport themselves to different locations
in the body. There are very small lymphocytes.
01:27
There are very large lymphocytes. They range
from roughly 6 to 8 microns to about 18 micronsin size. A granulocyte that is very important
to understand is the monocyte. It is a hugecell. It is about 18 to 20 microns in diameter
when you see it in a blood smear. Now again, theyare traveling through blood and they are not
doing anything within the blood itself.
01:57
It is only when they moved into connective
tissue that they do their job. They transforminto being a macrophage and we will learn
about these macrophages when we look at allthe tissues of the body and all the organs
of the body in more detail. They have a verycharacteristic indented nucleus, a bean-shaped
nucleus and that enables them to be identified,apart from their massive sizes well relative
to the other blood cells. Now again reflecton what I've said earlier about the orientation
of cells in the blood smear. You are lookingat a whole cell here. If that monocyte
that was rotated in another direction,you may not see that in indented nucleus, so it may
make it difficult to say that some monocytecould, in fact, be a mast cells travel through
the blood and they look like monocytes.
03:04
It is only when they move into the connective
tissue, those mass cells then accumulate thegranules that they use in their role as being
vasoactive agents and mediators.

About the Lecture

The lecture Blood: Lymphocytes and Monocytes by Geoffrey Meyer, PhD is from the course Connective Tissue.

Included Quiz Questions

What is the average size of lymphocytes?

6-18 microns.

6-8 microns.

5 microns.

2 microns.

0.5 microns.

When do monocytes become phagocytic cells?

When they enter connective tissue.

In blood.

In interstitial fluid.

In bone marrow.

Do not change into phagocytic cells.

Author of lecture Blood: Lymphocytes and Monocytes

Geoffrey Meyer, PhD

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